Don't forget Demolitions Vets. They can handle any armor with ease and their higher BS makes them deadly with Melta Guns.
Even Dreadnoughts and Land Raiders are afraid of them. After all, 10 guys with a Demo Charge, Melta Bombs and special weapons for less than the cost of an un-upgraded Dreadnought is bloody scary. Heck you get 70 points of explosives for less than half price! By itself that's a pretty sweet deal.
I'm building one right now with a Plasma Pistol, Melta Gun and 2x Grenade Launchers. I plan on dropping them off from a Valkyrie, but they should still be pretty effective on foot.